In a storage apparatus, a virtualization function for virtualizing a resource to efficiently utilize a physical disk region is occasionally used. For example, as a virtualization function, Thin Provisioning is known.
In the thin provisioning method, a region of a virtual disk is managed in a region called block of, for example, 512 KB and additional allocation to a physical disk is performed one by one block as occasion demands. In the thin provisioning method, when a virtual disk of a capacity (for example, 100 GB) requested by a user is created, all regions by 100 GB are not physically allocated at the same time with the creation, but a virtual region is dynamically allocated to a physical disk in a unit of a block in accordance with a capacity with which data is to be actually written.
It is to be noted that, as a related technology, a technology is known by which, when the thin provisioning technology is applied, a storage apparatus allocates a disk pool region to a logical disk in a different unit of allocation in response to whether the allocation policy set to the logical disk attaches importance to the speed or to the capacity. In the technology, if a writing request of data is received, then an I/O pattern is decided and the allocation policy is changed in response to the I/O pattern. Further, in the technology, re-arrangement of a data region is periodically performed in response to the allocation policy. For example, where the allocation policy is set to the attachment of importance to the speed, original data is copied into an allocated region and a data region before the copying is deleted such that non-successive data regions are determined as successive data regions.
In a virtual emulator, also a technology for retaining an operation situation of one or more kinds of virtual servers and another technology for analyzing an access pattern for successively or non-successively accessing data stored in a secondary storage apparatus to predict data to be accessed in the future and reading out the data in advance from a secondary apparatus into a main storage apparatus are known.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2010-86420
Patent Document 2: Japanese Laid-Open Patent Publication No. 2001-195270
Patent Document 3: Japanese Laid-Open Patent Publication No. 09-185462
Patent Document 4: Japanese Laid-Open Patent Publication No. 2008-186172
Patent Document 5: Japanese Laid-Open Patent Publication No. 02-77949
In the thin provisioning method, while a physical disk can be utilized efficiently, regions allocated to a virtual disk exist in a dispersed relationship in the physical disk. Therefore, in the thin provisioning method, a sequential I/O (Input/Output) performance sometimes degrades in comparison with a Thick Provisioning method by which the entire capacity of a virtual disk is allocated collectively to a physical disk.
Further, in the related technology described above, since decision of an I/O pattern and allocation of a disk pool region in accordance with an allocation policy are performed in response to a writing request, it takes time before data relating to the writing request is written into the disk pool region and a performance of a writing process degrades occasionally.